The present invention relates to a thermal transfer printer, more particularly, it relates to a thermal transfer printer which has a thermal head and a ribbon cassette mounted on a carriage and is arranged such that, at the same time as the carriage moves transversely, an ink ribbon within the ribbon cassette is wound during printing.
A thermal transfer printer has heretofore been known in which the power to wind the ink ribbon is obtained from the power which drives the carriage, and a mechanism for cutting off the ribbon winding power is provided (Japanese Patent Laid-Open No. 179680/1983).
The thermal transfer printer described above is provided with a drive transmitting mechanism which allows the ribbon feed roller of the ribbon cassette to rotate in interlocked relation to the movement of the carriage, and a clutch for cutting off the engagement between the drive transmitting mechanism and the ribbon feed roller. The feed of the ink ribbon is effected by the cooperation between the ribbon feed roller and a press roller, and the travelling speed of the ink ribbon is maintained at a predeterminedly constant value.
The present inventors examined an arrangement in which the ribbon feed roller and the press roller are eliminated, and the ink ribbon is wound by the take-up core of the ribbon cassette. It has been found as the result of the examination that, as the ink ribbon is wound, the roll diameter of the ink ribbon being wound up on the take-up core increases, which fact involves an undesirable change in the travelling speed of the ink ribbon and consequently leads to the occurrence of a rubbing transfer phenomenon.
The rubbing transfer phenomenon is known such as following phenomenon. Even at the moment that the thermal head is pressed against the platen through the transfer printing paper, the thermal head and the ink ribbon are moving horizontally. In consequence, the ink ribbon moving at that speed rubs against the transfer printing paper before stopping. More specifically, the ink ribbon slides on the transfer printing paper until the speed of the ink ribbon is zero. While the ink ribbon is sliding, the ink on the ink ribbon is separated therefrom and undesirably adheres to the transfer printing paper, thus smearing the paper.
At the moment the thermal head presses the ink ribbon against the thermal printing paper to start printing, the ink ribbon is undesirably dragged in the direction of carriage motion together with the thermal head, whereby the ink ribbon is rubbed against the transfer printing paper, thus smearing the paper.
It is also possible to prevent the rubbing transfer phenomenon by transversely moving the carriage, that is, the thermal head, after the thermal head has been completely pressed against the transfer printing paper and the pressing force has thus been obtained. However, when it is necessary to skip during printing, that is, when it is necessary for the thermal head to be separated from the platen and against it again to the thermal printing paper, there is a need to suspend the transverse movement of the carriage every time skipping is required, and this greatly reduces printing speed. It is not therefore possible in practice to employ such a rubbing transfer prevention method.